The National Investigations Committee on Aerial Phenomena (Nicap)

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# Approved For Release 2001/04/02 : CIA-RDP81R00560R000100010001-0 RADAR: THEORY & FACT be severely strained coincidence for an unidentifie

Except for cases of so-called "anomalous propagation"--false radar targets caused by bending or refraction of radar signals--UFO targets on radar constitute objective confirmation of the reality of unexplained objects in the atmosphere. Some research reports have tended to explain-away radar UFO sightings as "false targets. . . [sometimes caused by] a low angle radar beam . . . reflected from one surface to another before retracing its path to the radar." [66] Unexplained radar targets have been observed since the early days of radar.

Some evaluations of this phenomenon appear to be more a rationalization of troublesome reports than objective studies of them. Facts of observation seemingly are ignored or glossed over in order to make a theory fit. A prime example of this procedure is the study by the Civil Aeronautics Administration (CAA) of the famous July 1952 radar sightings over Washington, D.C. [67] The CAA report concludes that the Washington sightings were "ground returns caused by reflection phenomena closely connected with the temperature inversions in the lower atmosphere."

Table 1 of the CAA report, "Tabulation of Unidentified Radar Targets and Visual Objects Reported to Washington ARTC Center," includes one case for May, twenty-two for July, and 11 for August. Yet the text goes into detail on, and bases its conclusions on, only reports for the nights of August 14/15 and August 15/16. Unlike the July cases, there were no visual sightings on these nights and the recorded speeds were extremely slow (about 24-70 m.p.h.) The characteristics of the phenomena on these nights, and the lack of visual sightings, do resemble so-called "angels" (which are themselves little understood non-visual phenomena). By contrast, many of the July cases involved objects tracked in high-speed flight and also observed visually by pilots exactly where radar showed the objects to be.

Evaluations of this kind, aside from their glaring omissions of data and questionable reasoning, fail to take into account two vitally important points: (1) Because of the long history of false radar targets, they and their characteristics are well-known to experienced radar operators. (2) The bending of radar beams and creation of false targets on the scope cannot explain sustained radar-visual sightings. If a pilot sees a light source or object which changes its angular position radically, and ground radar shows a target maneuvering as described right where the pilot is looking, this cannot be explained in terms of the erratics of radar.

Because it is known that false targets do occur on radar screens which can be misinterpreted by inexperienced operators, radar-visual sightings in general are more significant evidence than reports lacking visual confirmation. As in all other aspects of UFO investigation, it is necessary to weed out erroneous reports and to recognize that human error is possible. But the same logic often applied to UFOs in general seems to be used by skeptics on radar cases: Because error is possible, and because some people definitely have been mistaken, all the reports are false. This is known as throwing out the baby with the bath-water.

## What Radar Shows

In general, a blip on radar always corresponds to a reflection off of some solid (or liquid) surface, though that surface may not be where the radar scope indicates it to be. The surface may be (a) a mass of raindrops in a cloud in the position where radar shows it to be; (b) a solid object in the air in the position where radar shows it to be; (c) something on the ground, reflecting back to the scope and only seeming to be an object in the air. The latter explanation commonly is invoked to account for all radar UFO reports.

This highlights the real problem of radar sightings: Interpretation of the scope by radar operators. The phenomenon most subject to misinterpretation is the 'ducting' effect, where low-angle radar beams are bent around the earth's curvature. An object which would ordinarily be out of radar range might then be detected, and mistaken for something which seems to be closer and in a different position. A radar set can pick up echoes of its beam which have bounced around from more than one reflecting surface, and back to the antenna. In a case of this type, it would

be severely strained coincidence for an unidentified object to be sighted visually in the same position as the false radar target.

## Weather Targets on Radar

Weather targets on radar may be ruled out generally as a source of false UFO reports. Clouds and cold fronts are not detected by radar, except for rain-carrying clouds, in which case it is the moisture (precipitation) which is detected. An Air Force manual on the subject states " . . . in general, strong radar echoes will be returned only from air of high specific humidity in which intense convective activity releases water in large amounts." [68] The echoes received are "false" only in the sense of not representing solid airborne objects. They are real liquid objects collectively acting as reflectors of the radar beam.

Section II, Paragraph 15 of the Air Force manual discusses "Interpretation of Echoes." In general, weather targets show up as diffuse masses on the radar screen, and their origin is easily recognizable.

Dense nimbostratus from which rain is falling, the manual states, can be detected to short or moderate ranges. "... echoes from nimbostratus usually appear on the PPI[Plan Position Indicator] scope as a mass of brightness concentrated about the center of the scope and merging into the blackness of the outer rings. . . there are many breaks and irregularities in the pattern since rain does not fall uniformly over even a small area."

## Radar Angels

A recent example of radar angels occurred at the NASA Wallops Island, Virginia, base during the Spring of 1962. The observations were analyzed by the Cornell University Center for Radiophysics and Space Research, for the Air Force Cambridge Research Laboratory. [69] The analysts theorized that "plate-like" objects could explain the observations, but commented: "It is difficult to conceive of foreign objects in the atmosphere having this plate-like shape. It is even more difficult to imagine that such objects would invariably maintain a consistent horizontal orientation while passing over the radar station. . ."

Although it is clear that radar angels have not been satisfactorily explained, the Center suggested that "most" of them were caused either by very smooth layers of refractive index gradient or by a single intense [atmospheric] discontinuity. . . "

What are radar "angels?" Used in its broadest sense, the term applies to all unidentified targets on radar. But this terminology is misleading, since the targets have been of three basic and distinct types: (1) Diffuse and intermittent targets probably attributable to meteorological effects; (2) Sharp, "solid" targets which give a persistent blip exactly like that of a moving metallic aircraft (sometimes also observed visually); (3) groups of targets, usually in very slow-moving meandering swarms, for which there are no known visual observations. We prefer to adopt the terminology of CSI, a UFO investigation group in New York City, and call the third type "angels;" the second "UFOs."

The research section of CSI has published an excellent analysis of radar angels; pertinent extracts are quoted here.

## "ANGELS" Explained by Two Experts (Two Different Ways)

Typical "angels" are characterized by being gregarious, slow-traveling (30-60 mph.), and much more conspicuous to radar than to the eye - in fact, it may be that no one has ever seen them except on a radarscope. They have been observed ever since 1943, when microwave radar was first being developed, and they have never been acceptably explained.

The celebrated Washington radar sightings of July 1952 occurred during a period when typical angels were being seen there abundantly (for details, see C.A.A. Technical Report #180, Note 67). . .

The radar visibility of birds happens to be known; it is very much less than that of angels. Birds (and a fortiori, flocks of birds) can be detected on a powerful radar set - at distances up to a mile or two. Bonham and Blake, authors of an earlier claim that angels could be identified with birds (Scientific Monthly, April 1956), admitted that the visually-confirmed birds